1. Field Of The Invention
This invention relates to a part or tool moving unit. More particularly it relates to a linearly movable carriage which is moved on ways for precise positioning which is operated in an atmosphere containing abrasive particles.
2. Description Of The Prior Art
In my U.S. Pat. Nos. 4,550,551, 4,553,375, 4,569,183 and 4,722,169 I have set forth the operation of the various elements and mechanisms utilized in a conveying and part transfer or loader system in which powder compacted articles such as spark plug bodies or insulators are conveyed from a compacting press to be automatically loaded in a specific arrangement of rows in a sagger. The sagger is then conveyed to and through a firing or sintering furnace to transform the "green" bodies held together by a binder into finish stable parts. Often inserts are used in the sagger to properly position and hold the bodies in alternate staggered rows. All this requires precision detection and positioning of the sagger and insert coupled with precise pick up of the parts by a loader and movement of precise distances to perform the loading. One of the key mechanisms of this system is the part pick up unit which employs a slide or carriage which must be rapidly reciprocated, smoothly and precisely. Such precision and smooth operation is obtained by supporting the carriage on cylindrical ways by the use of linear ball bearings.
Unfortunately the fine aluminum oxide powder from which the bodies are pressed is abrasive and gets into the atmosphere from part breakage and handling abrading. This eventually causes failure of the ball bearings. Even with improvements in bearing design, for example, by substituting nylon balls for the commonly used steel balls, the life can be relatively short. With a bearing using steel balls failure can occur in as little as 100,000 cycles whereas with the use of nylon balls this life can be increased to 750,000 to one million cycles. However with a handling speed of one part per second, failure can occur in one month or less. Various sealing and purging techniques have been attempted to improve life with little success. It is to the solution of this limited life problem for a linear actuater that the present invention is directed.